Here is my guess.
Scratch that. I never thought about heights. When I was reading I didn't imagine up a measuring stick! This is my chart.
From Tall to Short
Ax, Jake, Rachel, Tobias (human), Marco, Cassie, Tobias (bird)
Jake and Rachel were the same height. Ax was higher than them because his lower section is like a young horse, plus a teenagers chest. WAAY taller. Tobias was always just slightly shorter than Rachel. Very slightly. Marco was about an inch shorter than Tobias. Cassie and Marco were the same height. Give or take a centimeter. And then, of course, a red tailed hawk isn't even a yard tall.